This invention relates to a method and apparatus for spiral spray coating and has for its object to widen the coating width by forming a spiral spray coating pattern by the process of causing a rotating spray flow of pressurized air (rotating air jet centering an adhesive hole in plan view) to act on hot melt adhesive bead extruded form the center of a nozzle tip.
As to the method of spiral spray coating and apparatus therefore, Tokukaisho No. 61-200869 (Method and apparatus for spraying a molten adhesive agent) has been well known. This laid-open patent specification discloses the coating art whereby the width of coating on material is enlarged by coating in a spiral spray pattern which is obtained by causing a rotating jet of pressurized air to act on a hot melt adhesive bead being extruded form an adhesive hole of a nozzle.
In the above prior art, however, in the case where viscosity of hot melt adhesive agent to be fed is high, rotation of a spiral spray pattern lowers extremely due to high viscosity of heated and molten hot melt adhesive agent extruded from an adhesive hole of a nozzle apparatus and consequently a filamentous spiral pattern as shown by H0 in FIG. 17, instead of a spiral rotating pattern, is formed.
Thus, a spiral spray pattern coating cannot be expected. Moreover, as shown in FIG. 18, a grain p (also referred to a shot, a hook or the like) is formed at the start of spray coating. This grain p settles on the coating surface of a material (film, for instance) and makes a hole in the material by melting. Thus, merchandize value is lowered. In the case of intermittently repeated coating, this grain p is dispersed at each spraying and soils a coating line and a coating workshop.
Furthermore, referring to FIG. 18, problem is that in spiral spray coating by the spiral spray coating apparatus, accompanying air Ka occurs outside the pressurized air flow (spiral air) K1. This accompanying air Ka amounted to more than 10 time more than the pressurized air flow (spiral air) K1, with the result that oil parts and low molecule parts of a hot melt adhesive cling to and around a top end of a nozzle tip in the shape of micro-sized fiber. Thus, paper dust in the workshop cling to and around a nozzle hole and collects there. As a result, such troubles as the loss of working time caused by replacement of a clogged nozzle and manufacturing of inferior products (due to collected paper dust falling on and mixing in material) are inevitable.
Regarding a spiral spray coating method and an apparatus therefore, Tokukaihei No. 3-146160 (Method and apparatus for hot melt adhesive coating) is also well known. This laid-open patent specification discloses a spray pattern coating by causing rotating spray (whirling flow) of pressurized air to act a hot melt adhesive being extruded from an adhesive hole of a nozzle, similar to the above-mentioned Tokukaisho No. 61-2000869 and also the present invention. This patent specification discloses formation of a non-conical spiral pattern (an elliptical pattern) and a pattern of small and large elliptical shapes connecting alternately by blowing air against a spiral bead from the side direction. Although this apparatus has the second compressed air holes, it does not settle the problems of dispersing particles p and accompanying air Ka.
Both Utility Model Official Gazette No. 30470146 (Coating gun apparatus) and No. 3048747 (Coating gun apparatus) disclose the second air flow which is formed by means of a hood surrounding a jet nozzle body and compressed air exhausting holes made at the circumferential part of said hood. According to this gun apparatus, open air flowing-in holes are made in horizontal direction against a spray nozzle body so that the open air from the open air flowing-in holes is caused to act on coating liquid from the spray nozzle body, whereby coating liquid is dispersed in the shape of microsized particle while it is regulated in the coating direction and coating scope by the hood. Therefore, this apparatus does not relate to the spiral spray coating by forming a spiral splay coating pattern by the process of causing a rotating spray flow of pressured air (rotating air jet centering an adhesive hole in plan view) to act on hot melt adhesive bead extruded from the center of a nozzle hole, which is the object of the present invention. It is true that this apparatus has the effect of limiting the coating range by forming an air curtain by pressurized air (the second air flow) extruded from the circumferential part of the hood but does not settle the problems of dispersing particles p and accompanying air Ka. Because it is free from the problems of dispersing particles p and accompanying air Ka shown in FIG. 18 due to non-existence of the composition of a horizontal bottom surface of the nozzle tip. Further, this apparatus does not have the action and effect of obtaining a regular coating width and a well-formed spiral spray coating pattern by coursing an auxiliary pressured air flow from plural second pressurized air holes to act on a spiral coating pattern rotating at high speed.
An object of the present invention is to provide a method and an apparatus for spiral spray coating, whereby even high viscosity hot melt adhesive and resin are available for coating in a spiral spray pattern of high-speed rotation and also a regular coating width and a regular spiral spray pattern can be obtained.
Another object of the present invention is to make the particle p as small as possible and confine the setting point of particles p within the range of a spiral rotating pattern.
Still another object of the present invention is to prevent occurrence of accompanying air in spiral spray coating.
The first invention of the present application provides that, in the method of spiral spray coating, whereby a spiral spray pattern is formed by causing a rotating jet of pressurized air extruded form a plurality of pressurized air holes disposed circularly in close proximity to an adhesive hole at the bottom side of a nozzle tip to act on a hot melt adhesive bead being extruded from an adhesive hole opening at a projecting part at the center of the bottom side of the nozzle tip, a method for spiral spray coating characterized in that it comprised by forming the second pressurized air flow, which is extruded from many second pressurized air holes located concentrically around the first pressurized air holes, at the outside of the first pressurized air flow which is extruded from many first many first pressurized air located concentrically around an opening of an adhesive hole, by forming a circular air curtain concentric with the center of a spiral by the second pressurized air flow K2 which is fed to the outside of the first pressurized air flow (spiral air).
The second invention of the present application is characterized in that, in the first invention, the second pressurized air flow K2 is supplied independently of the first pressurized air flow K1.